1. Field of the Invention
The present invention relates to a push button switch, and more particularly, to a structure of a push button switch with a display device which is suitable for use in an apparatus operated with high frequency, has a long life, and is capable of stable and smooth operation.
2. Description of the Related Art
In the conventional push button switch, resins with high durability such as polyacetal resin or fiber reinforced plastic are generally used in sliding parts between an operational button and a switching body. In addition, in an apparatus which is used with high operation frequency and requires a smooth operation feeling, a lubricating agent such as grease is applied to the sliding part.
Even if a plunger and a case formed of a resin with a small friction coefficient are used, when used as a push button switch in an apparatus with high operation frequency, problems happens in durability such as wear-out of the resin surface due to mutual friction of resin, an increase in looseness of the operational button, and degradation in the operation feeling due to the looseness of the operational button. Especially, constantly stable operation force and operation feeling are required for the push button switch used in the field of a broadcasting apparatus. Furthermore, a market requires a push button switch having fairly good operability so as not to give any fatigue to fingers during the operation.
In addition, the present applicant has developed a push button switch which generates smooth operation feeling by disposing round pins between a case and a plunger, and by moving the plunger against the case along the round pins as rails (See Patent Document 1 below).
On the other hand, as for a display device, an STN liquid crystal is used, which has problems such as complicated configuration and increased consumption of electric power due to a need for a backlight. In addition, there exists another problem that the viewing angle is narrow.
[Patent Document 1] Japanese Patent Application Publication No. 2005-93254
In the conventional push button switch with round pins as rails, engaging grooves are provided longitudinally on the inner wall of the case and on the outer wall of the plunger, respectively, and the round pins are freely fit to the engaging grooves.
Due to the use of a liquid crystal as a display device, there is a problem such as complicated configuration due to a need for a backlight. In addition, there exist other problems relating to the liquid crystal such that the viewing angle is narrow and that consumption of an electric power is not negligible.
In light of the foregoing, it is an object of the present invention to provide a push button switch with a display device which has a long life, high stability in operation to keep the initial operation force and operation feeling unchanged, and a wide viewing angle, and which is capable of reducing the electric power consumption and simplifying the configuration.